Method of starting forced-flow steam producers



Feb. 13, 1968 K. KNIZIA 3,368,533

I METHODOF STARTING FORCED-FLOW STEAM PRODUCERS Filed'Feb. 14, 1966 2Sheets-Shet 1 INVH/TUB Feb. 13, 1968 K. KNIZ |A 3,368,533

METHOD OF STARTING FORCED-FLOW STEAM PRODUCERS Filed Feb. 14, 1966 2Sheets-Sheet 2 WVE/VTUH United States Patent 3,368,533 METHOD OFSTARTING FORCED-FLOW STEAM PRODUCERS Klaus Knizia, Nochen uberEngelskirchen, Germany, as-

signor to L. & C. Steinmuller G.m.b.H., Gummersbach, Germany Filed Feb.14, 1966, Ser. No. 527,001

Claims priority, application Germany, Feb. 13, 1965,

St 23,363 11 Claims. (Cl. 122406) ABSTRACT OF THE DISCLOSURE The presentinvention relates to a forced-flow steam producer having main conduitmeans adapted to be connected to a steam consumer and comprising feedwater supply means and evaporator heating surface means communicatingtherewith and also comprising first and second superheater heatingsurface means in series with each other and with said evaporator heatingsurface means, and furthermore including first circuit means shuntingsaid evaporator heating surface means and comprising a steam and waterseparating vessel and a pump while second circuit means lead from apoint of said main conduit means between said evaporator heating surfacemeans and said feed water supply means to a point of said main conduitmeans between said first superheater heating surface means and saidevaporator heating surface means. This arrangement is provided withcontrol means which permit operating the two circuits steamwise duringthe start of the steam producer in parallel arrangement with each otherand subsequently with increasing firing of said steam producer tocontinuously operate the second circuit and the first superheaterheating surface means steamwise in series with each other.

The present invention relates to a method of starting forced-flow steamproducers, especially steam producers which operate at a high life steampressure and with one or multiple intermediate superheating stages.

With increasing regenerative preheating and the employment of a singleor multiple intermediate superheating stage of high live steam pressure,the proportion of the feed water preheater and evaporator heatingsurfaces in the boiler is reduced in favor of superheatin-g surfaces. Asa result thereof, the high pressure superheater and the heating surfacesof the first intermediate superheater have to extend deeply into thefirst flue of the boiler.

When starting such a boiler, there exists the necessity ofsatisfactorily cooling the said superheating surfaces in order toprevent too fast a temperature increase which otherwise, particularlywhen high heat resistant materials are employed, would cause theformation of tears and cracks. The heretofore known employment of acirculatory system for the evaporator heating surfaces with or withoutthe merging portions, with which subsequently the produced steam passesbetween the superheater surfaces will not suffice under modernconditions to sutficiently cool the superheater parts.

It is, therefore, an object of the present invention to provide a methodof starting forced-flow steam producers, which will overcome the abovementioned drawbacks.

It is another object of this invention to provide a method of startingforced-flow steam producers which while assuring a sufiicient cooling.of all boiler parts including the evaporator heating surfaces, theadjacent superheater surfaces and the intermediate superheater orsuperheaters, will while maintaining an admissible temperature gradient,make possible a gradual heating up of said boiler parts,

and a stepwise putting into operation of the heated up boiler parts forthe normal boiler operation.

These and other objects and advantages of the invention will appear moreclearly from the following specification in connection with theaccompanying drawings, in which:

FIG. 1 is a diagram showing a plurality of circulatory systems onheating surfaces which when in operation are arranged in series withregard to each other.

FIG. 2 shows a diagram illustrating one circulatory system only and aplurality of bypass conduits which permit a liquid cooling of the firstsuperheating surface during the starting of the boiler.

The objects outlined above have been solved according to the presentinvention by parallelly arranging the evaporator heating surface and thefirst superheater surfaces during the first starting phase with regardto the conducting away of the steam produced in said two heatingsurfaces. At the same time, the water separated from a steam watermixture leaving the evaporator heating surface is in a separating vesselconveyed to the first superheater surfaces. When the quantity of steamproduced in the evaporator heating surface has reached a certainmagnitude and when the evaporation point of the residue in the firstsuperheater surfaces has dropped to approximately the start of theheating surface, the evaporator heating surface is directly connectedwith the first superheater surfaces so that the steam freed in theseparating vessel will now cool all superheater surfaces one after theother. At the same time, a conduit leading from the water side to thefirst superheater surfaces is closed. The steam freed in the separatingvessel will now no longer bypass the first superheater surfaces.

According to a further development of the present invention, the methodaccording to the invention will be further improved by providing afurther phase which precedes said first phase and according to which theevaporator heating surface and the first superheater surfaces are withregard to the feed water supply and the circulation first arrangedparallelly and subsequently serially and in continuous transition. Thus,at the first phase of the starting operation, feed water will becirculated in the circuit which includes the evaporator heating surface,and in the circulatory path which includes the first superheatersurfaces. With increasing firing, feed water heated in the boiler iswithdrawn from the circulatory circuit which cools the evaporatorheating surface, and this feed water is conveyed into the circulatorypath for the first superheater surfaces. The water which evaporates inthe first as well as in the second circulatory path is replaced by thefeed water pump which pumps water into the first circulatory path. Aftera further increase in the firing, finally the second circulatory pathfor the superheater surfaces is turned off and the saturated steam orthe mixture of liquid and saturated steam derived from the evaporatorheating surface is directly employed for cooling the superheatersurfaces adjacent the evaporator. Instead of being circulated in acirculatory path including the first superheater surfaces, the waterafter having been circulated in the circulatory path of the evaporatormay also be passed separately through the first superheater section. Ifone of the two circulatory pumps should break down, the system may alsobe started with one circulatory pump only. If the circulatory pump inthe evaporator circuit remained inoperable, the starting of the systemis effected with one circuit in which similar to the heretofore knownmanner the evaporator is cooled and all of the steam freed in theseparating vessel is passed into the superheater surface following theevaporator. If, on the other hand, the circulatory system which includesthe first superheater surface remained operable, a circulatory paththrough the evaporator and the superheater heating surface is employed"while the circulatory system for the evaporator is turned off.

When installing intermediate superheater heating surfaces which duringthe starting of the boiler have to be cooled, the steam produced in theevaporator heating surface and in the first superheater surfaces maypartially be conveyed directly to the intermediate superheater orsuperheaters for purposes of cooling while said steam partially bypassesthe high pressure superheater. By varying the way in which the steamflow is split up, it is possible in combination with the customaryinjection to heat up all superheater surfaces at a maximum temperaturegradient.

The method according to the present invention permits on one hand tocontrol the temperature increase in the boiler heating surfaces whichare arranged in the combustion chamber and in the firebox whereby thearrangement will also be suitable for an automatic starting of steamproducers, and on the other hand, in view of the cooling of the fluegases on the first large heating surfaces which are passed through byliquid, the superheating surfaces which are cooled to a lesser degreeduring the phase of the starting operation will be subjected to lessstress.

Referring now to the drawings in detail, both circuits Show thepossibility of serially arranging heating surfaces which were firstarranged in parallel with regard to each other, and to effect saidarrangement in series continuously and without a temperature jump.

Referring first to the diagram of FIG. 1, feed water is conveyed by afeeding pump 2 through a feeding conduit 1 into the evaporator part 11.The evaporator heating surface 11 is followed by the first superheaterheating surfaces 21. From here the steam passes through the subsequentsuperheater heating surfaces 31 and 41 to the main steam conduit 51which leads to a turbine. From said turbine a conduit 38 passes to thefirst intermediate reheater 34 while a further conduit 54 leads back tothe turbine. Another conduit 48 leads from the turbine to the secondintermediate reheater 44 from which a conduit 58 leads back to theturbine. Behind the evaporator heating surface 11, at point 13, there isbranched off a circulating conduit 14 which leads to a separating vessel10. Water is withdrawn from vessel 10 through a conduit 9 which at 49leads back to the main conduit 1. The circulating conduit 14, 9 hasinterposed therein the separating vessel 10 and a circulatory pump 12and a control valve 8 arranged between circulatory pump 12 and point 49.The separated steam is conveyed from separating vessel 10 through aconduit 18 and a control valve 24 behind the superheating surfaces 21 tothe main conduit 1 at point 27.

At point 39 of feeding conduit 1 there branches off a conduit whichwhile bypassing the evaporator heating surface 11 leads into mainconduit 1 at point 4 ahead of the superheating surfaces 21. Conduit 5may by means of a control valve 3 selectively be shut off. Behind thesuperheating surfaces 21 at point 16 there branches off a circulatingconduit 19 which at point 45 leads into the bypass conduit 5. Thecirculating conduit 19 has interposed therein a separating vessel 20-and a circulatory pump 22. The steam separated in the separating vessel20 is through conduit 28 and conduit 29 likewise conveyed to the mainconduit 1 into which it leads at point 47. This connecting conduit hasinterposed therein a control valve 57. Thus, the system comprises afirst circulating circuit composed of feeding conduit 1, evaporatorheating surface 11, conduit 14, separating vessel 10, circulatingconduit 9, and circulatory pump 12. The second circulating circuitcomprises the first superheater heating surfaces 21, the circulatingconduit 19, the separating vessel 20, the circulatory pump 22, and aportion of the feeding conduit 5. Both circulating circuits arecompletely separated from each other and may be operated separately fromeach other. The separated steam is in conformity with the abovedescribed circuit passed from both circulating circuits to the mainconduit 1 ahead of the superheater heating surfaces 31. At point 59, aconnecting conduit 6 branches off from circulating conduit 9, whichconduit 6 leads at 55 into the branch conduit 5. Conduit 6 hasinterposed therein a control valve 7. The water withdrawn from theseparating vessel 10 can thus through said conduit 6 in a controlledmanner be conveyed to feeding conduit 5 and thus to the firstsuperheater heating surfaces 21.

Conduit 1 also comprises a check valve 63 which is arranged ahead of thepoint where circulating conduit 9 leads into conduit 1 but ahead ofpoint 49. Another check valve 63 is arranged in conduit 5. A shut-offvalve 23 is adapted to separate the first superheater heating surfaces21 from the second superheater heating surfaces 31. This valve 23 isarranged behind the shut-off point 16 of the circulating conduit 19 butahead of point 47 where conduit 29 leads into the main conduit 1.Finally, the steam conduit 18 communicates with main conduit 1 through aconduit 15 having interposed therein a shut-off valve 17 and branchingoff from conduit 18 at point 62. Conduit 15 leads into main conduit 1 atpoint 4.

A conduit 35 branches off main conduit 51 at point 52. Conduit 35establishes communication between conduit 51 and conduit 38 through theintervention of a control valve 30, conduit 38 leading to the firstintermediate reheater 34. A conduit 54 leads from the first intermediatesuperheater 34 to the above mentioned turbine while at point 53 aconduit 45 branches off from conduit 54 and establishes communicationbetween conduit 54 and a conduit 48 leading from the turbine to thesecond intermediate reheater 44, a control valve 40 being interposed inconduit 45. A conduit 26 branches off from conduit 18 and has a shutoffvalve 25 interposed therein. Conduit 26 leads at point 61 into conduit29 which latter behind point 61 at point 56 branches into two conduits33 and 43 each of which has a control valve 32, 42 respectively arrangedtherein. The first conduit 33 leads at point 50 into the branch conduit35, whereas the second conduit leads at point 60 into the branch conduit45. By means of these two conduits, conduit 118 communicates with theintermediate reheaters 34 and 44 so that the steam separated in theseparating vessel 16 is able to cool these intermediate superheaters.Through conduits 28 and 29 steam from the separating vessel 20 may beconveyed to the intermediate superheaters 34 and 44.

With the diagram according to FIG. 1, during the starting phase, firstthe feeding pump 2 fills the circulating system for the evaporatorheating surfaces 11 and the circulatory system for the superheatingsurfaces 21. Prior to firing the boiler, also the pumps 12 and 22 arestarted, and a separate circulating operation is started. At this point,the evaporator heating surfaces 11 with the circulating circuit14-10-9-12 are in parallel with the superheating surfaces 21 with thecirculating circuit 19- 20225, while feeding water is continuouslyconveyed through feeding conduit 1 to the first circuit and to thesecond circuit. The steam produced in the circulating system of theevaporator heating surface 11 is separated in separating vessel 10 andthrough conduit 18 and control valve 24 is conveyed to the secondsuperheater heating surfaces 31 which are located behind the superheaterheating surfaces 21 cooled by the second circulating system.

The increase in the evaporator heating surface 11 according to thisdiagram by the heating surface of the first superheater 21 which in thisphase of the starting operation acts as evaporator, not only produces asuflicient cooling :for these heating surfaces 21 but also brings aboutthat at an early stage a sufficiently large quantity of steam will beobtained for cooling the successive superheaters 31, 41, and reheaters34 and 44.

With increasing firing, valves 3 and 8 are throttled, and valve 7 isopened in a corresponding manner. As a result thereof, the proportion ofthe evaporated water which is replaced by the feeding pump willgradually alone be in communication with the evaporator heating surface11. The superheater heating surfaces 21 are to an ever increasing extentsupplied with the water which is withdrawn by pump 12 in boilingcondition from the separating vessel and which is then through controlvalve 7 and conduit 6 conveyed to conduit 5. However, if desired, vessel10 may from the very start, with control valve 3 of the circulatingcircuit of the heating surfaces 21 closed, be filled through valve 7 andconduit 6 and be charged during the starting operation so that as far asthe water flow is concerned arrangement in series is maint-ained. 7

With further increasing firing, the quantity of steam freed inseparating vessel 10 will eventually become so great that it will besufficient to properly cool the superheater heating surfaces 21 and allof the subsequent heating surfaces. The steam freed in vessel 10 willthen no longer be passed to the superheaters 31, 41, and reheaters 34,44 through control valves 24 and but will through control valve 17 andconduit 15 be conveyed to the start of the superheater heating surfaces21. At this time the circulating system 19-20-22-5 of the firstsuperheater heating surfaces 21 is taken out of operation. Notemperature shock will occur at the feed-in point to said heatingsurfaces 21 because the water in boiling condition is replaced bysaturated steam of the same temperature. From this time on, the startingoperation of the steam producer will take its course as is customarywith the systems with circulation.

When the circulating system of the evaporator circuit 11 has dropped outdue to a disorder, it is also possible to start the steam producerthrough the intervention of the circulating system of the superheaterheating surface 21 by blocking the check valve flap 63 so as to maintainthe same in open position. In these circumstances, a circulating circuitis obtained via the heating surfaces 11 and 21 and the circulatingsystem 192022-5 and control valve 3 back to feeding conduit 1.

Referring now to FIG. 2, this figure shows an arrangement which is basedon the same principle as the system of FIG. 1 with the exception thatthe second circulating system of FIG. 1 is modified over that of thearrangement of FIG. 2. According to FIG. 2, the circulating system1410911 of the evaporator is filled and brought into operation throughfeeding conduit 1. A portion of the feeding water passes through controlvalve 3 and conduit 5 to superheater heating surfaces 21. While valve 23is closed, said feeding water passes through conduit 29 and controlvalve 37 as well as conduit 36 into the open or into a startingexpander. The first superheater heating surfaces 21 may also be filledthrough valve 7 and conduit 6, 5. With increasing firing, the proportionof the cold feeding water is reduced through valve 3 and conduit 5 tothe superheater 21 so that eventually through valve '7 and conduit 6only boiling water will be conveyed to the heating surfaces where itwill be evaporated.

It is also possible from the very start to press all of the water supply'by the feeding pump into the evaporator heating surface 11 and tosupply the heating surfaces 21 solely through valve 7 and conduit 6 fromthe circulating system of the evaporator heating surface. When the heatabsorption in the heating surfaces 21 is so great that the waterentering the same evaporates, valve 37 is closed, and steam is conveyedthrough valve 23 to the intermediate high pressure superheaters or asthe case may be through valves 32 and 42 to the intermediatesuperheaters for purposes of cooling. The steam separated in separatingvessel 10 of the circulating system is from the very start throughconduit 18 and valve 24 conveyed to the subsequent superheaters forcooling purposes. A corresponding splitting up of this steam to the highpressure and the intermediate superheaters is not shown in FIG. 2, butcan be realized in a manner analogous to that shown in FIG. 1. From acertain starting condition on, valve 7 will be closed and thecirculating operation is started through valve 8 into the feedingconduit and the evapoartor heating surface as is customary withheretofore known circulating methods. The steam freed in the separatingvessel is no longer through conduit 18 and valve 24 conveyed to thesuperheater behind the superheating surface 21 but through valve 17 andconduit 15 also the heating surfaces 21 are enclosed into the cooling bysaid saturated steam. From this time on, the starting of the steamproducer is continued as it is customary with boilers having acirculating system.

It is, of course, to be understood that the present invention is, by nomeans, limited to the methods set forth above but also comprises anymodifications within the scope of the appended claims. In thisconnection it should be noted that the circuits set forth above can alsoin an analogous manner be employed for stopping the steam producer.

What I claim is:

1. In a circuit for facilitating the starting of a forced flow steamproducer: feed water supply means, main conduit means adapted to beconnected with a steam consumer and to communicate with said feed watersupply means, evaporator heating surface means interposed in said mainconduit means, first superheater heating surface means likewiseinterposed in said main conduit means and arranged in series with andbehind said evaporator heating surface means when looking in thedirection of flow of fiuid through said main conduit means, secondsuperheater heating surface means also interposed in said main conduitmeans in series with and behind said first superheater heating surfacemeans when looking in the direction of How of fluid through said mainconduit means, first circuit means shunting said evaporator heatingsurface means and leading from said main conduit means at a pointbetween said evaporator heating surface means and said first superheaterheating surface means to a point between said feed water supply meansand the adjacent side of said evaporator heating surface means, saidfirst circuit means including a separating vessel adapted to separatesteam and water from each other and also including a circulating pump,second circuit means connected to said main conduit means at a pointbetween said evaporator heating surface means and said first superheaterheating surface means and also connected to said main conduit means at apoint between said feed water supply means and said evaporator heatingsurface means, and control valve means respectively located in saidfirst and second circuit means for controlling the same.

2. A circuit according to claim 1, in which said second circuit meansshunts said first superheater heating surface means and includes aseparating vessel for separating steam and water from each other andalso includes a circulating pump.

3. A circuit according to claim 1, which includes valve means adaptedselectively to be closed and opened and located between said first andsecond circuit means on one hand and said second superheater heatingsurface means on the other hand.

4. A circuit according to claim 1, which includes first auxiliaryconduit means leading from said separating vessel to said secondsuperheater heating surface means while bypassing said first superheaterheating surface means and said second circuit means, and valve meansinterposed in said auxiliary conduit means and adapted selectively to beopened and closed.

5. A circuit according to claim 4, which includes second auxiliaryconduit means leading from said first auxiliary conduit means to saidfirst superheater heating surface means, and valve means interposed insaid second auxiliary conduit means and adapted selectively to be openedand closed.

6. A circuit according to claim 4, which includes reheater means, andwhich also includes additional conduit means leading from said firstauxiliary conduit means to said reheater means, and valve meansinterposed in said additional conduit means for controlling the same.

7. A circuit according to claim 2, which includes reheater means, andwhich also includes: third conduit means branching off from the pressureside of the circulating pump in said second circuit means andcommunicating with said main conduit means at a point between saidevaporator heating surface means and said first superheater heatingsurface means, fourth conduit means leading from said separating vesselin said second circuit means to said reheater means, and valve meansinterposed in said third conduit means for controlling the same.

8. A circuit according to claim 2, which includes two branch linesrespectively branching off from said first and second circuit meansbetween the respective separating vessel and pump pertaining thereto.

9. A circuit according to claim 1, which includes conduit meansconnected to that end of said first superheater heating surface meanswhich is remote from said evaporator heating surface means, said lastmentioned conduit means being adapted selectively to be connected to astarting expander or to the outside of said steam producer.

10. A circuit according to claim 1, which includes first and secondreheater means, high pressure conduit means connected to the output sideof said second superheater heating surface means, a first feeding linefor said first reheater means connected to said high pressure conduitmeans, a second feeding line for said second reheater means connected tothe outlet side of said first reheater means, pressure reducing valvemeans respectively interposed in said first and second feeding lines,and conduit means adapted to communicate with said first and secondcircuit means and respectively leading into said first and secondfeeding lines.

11. In a method of starting a forced-flow steam producer having mainconduit means adapted to be connected to a steam consumer and comprisingfeed water supply means and evaporator heating surface meanscommunicating therewith, and first and second superheater heatingsurface means in series with each other and with said evaporator heatingsurface means, said steam producer also including first circuit meansshunting said evaporator heating surface means and comprising a steamand water separating vessel and a pump and also including second circuitmeans leading from a point of said main conduit means between said feedwater supply means and said evaporator heating surface means to a pointof said main conduit means between said first superheater heatingsurface means and said evaporator heating surface means, which includesthe steps of: during the start of said steam producer operating said twocircuits steamwise in parallel arrangement with regard to each other,and subsequently with increasing firing said steam producer continuouslyoperating said second circuit means and said first superheater heatingsurface means steamwise in series with regard to each other.

References Cited UNITED STATES PATENTS 3,038,453 6/1962 Armacost 1224063,120,839 2/1964 Glahe l22406 3,175,367 3/1965 Gorzegno et al l22-4063,194,219 7/1965 Hanzalek l22406 KENNETH W. SPRAGUE, Primary Examiner.

